Figure 4.

MR detection concepts of HP contrast agents. a) In vivo administration of HP 1-¹³C-pyruvate leads to its in vivo uptake as well as its subsequent metabolism to 1-¹³C-alanine (using alanine transaminase [ALT]), 1-¹³C-lactate (using lactate dehydrogenase [LDH]), which can be differentiated using ¹³C chemical shifts, and b) detected using Chemical Shift Imaging (CSI) to simultaneously produce multiple metabolic maps. Note the red (lactate), blue (alanine) and green (pyruvate) color coding in a) and b). c) Trigonometric dependence of observed (sine) and remaining (cosine) magnetization as a function of RF pulse excitation (or “tipping”) angle. d) Fundamental blocks of RF pulse sequences for conventional MR (top); hyperpolarized (HP) MR with fixed small-angle encoding pulses (middle), and HP MR with variable-angle encoding pulses (bottom).